U.S. Pat. No. 4,585,391 makes known a counter-torque device with ducted tail rotor and ducted flow-straightening stator for a helicopter, including a duct of axis substantially transverse to the helicopter, and in which are located, on the one hand, the rotor, substantially coaxial with said duct and generating a transverse flow of air and, on the other hand, the flow-straightening stator, including a plurality of profiled vanes fastened inside the said duct downstream of the rotor with respect to the flow of air and arranged in substantially radial fashion with respect to the said duct so as to be able to recover rotational energy from the flow of air at the exit from the rotor in the form of a counter-torque axial thrust adding to that produced by the rotation of the rotor within the duct, without increasing the power transmitted to the rotor for this purpose.
U.S. Pat. No. 4,585,391 also proposes for the vanes of the flow-straightener to extend between a stationary central body substantially coaxial in the duct and the annular wall of the fairing duct, and for them to provide alone the mechanical link between this stationary body and said wall, and therefore the fastening of the stationary body and of the rotor, mounted so that it can rotate on this body, within the duct, as replacement for support arms, often numbering three, generally used to provide this mechanical link between the stationary body and the wall of the duct.
It is further proposed in the abovementioned patent for the duct to exhibit, from the upstream end to the downstream end, a convergent inlet with rounded edge, a cylindrical part, in which the blades of the rotor rotate, and a divergent nozzle ending in a divergent outlet, the flow-straightener being located within the divergent nozzle, and it being possible for the vanes which constitute it to be independent of one another and to have a constant aerodynamic profile and zero twist, for example a profile of the NACA 65A10 type.
Such a flow-straightener with profiled stationary vanes simultaneously fulfils several functions and gives significant advantages:
from the aerodynamic and acoustic standpoints, the vanes straighten out the airflow leaving the rotor and thus enable some of the rotational energy of the airflow to be converted into additional counter-torque thrusts, and the replacement of the known support arms [most often cylindrical and of relatively significant diameters, bathed in the flow from the rotor and constituting one of the significant sources of noise of the device due to the noise of interaction between the rotor and support arms] with profiled vanes decreases the drag while reducing the acoustic emissions of the ducted device; PA1 from the standpoints of the transmission of loading and rigidity, the flow-straightener connecting the structure of the helicopter to the mechanical assembly mounted in the duct makes it possible to transmit all the loadings from the hub of the rotor, from the rear transmission box (for the rotational drive of the rotor) and from the collective pitch control of the blades of the rotor to the wall of the duct, these loadings being better distributed by the vanes in the fairing, so that the use of ribs for taking up load in the latter proves pointless, the flow-straightener increasing the rigidity of the assembly owing to the fact that its vanes provide more numerous points for taking up loads on the wall of the duct than a conventional tripod of support arms. PA1 a duct, of axis substantially transverse to the longitudinal axis of the aircraft, and passing through the rear part of the aircraft in which part it is delimited by an annular wall, PA1 a rotor mounted substantially coaxial in the duct and driven in rotation by a mechanism fastened substantially coaxially in the duct so that the rotation of the rotor generates an airflow in the duct, and PA1 a flow-straightening stator, fastened into the duct downstream of the rotor with respect to the direction of airflow, and including an annular central body surrounding the rotational-drive mechanism, as well as vanes each one exhibiting a main vane section with aerodynamic profile straightening out the airflow down-stream of the rotor towards the axis of the duct, and extending between a vane root and a vane tip at its ends, and via which the vane is fastened respectively to the central body and to the annular duct wall, so as to support the rotational-drive mechanism and the rotor in the duct, and the vane is characterized in that it is composite and its main vane section exhibits laminated suction face and pressure face parts each comprising a pile of at least three layers of reinforcing fibres, essentially made of carbon, made rigid by a thermosetting synthetic agglomerating resin, at least one of the layers, either the internal one or the external one, of the pile comprising two sets of essentially unidirectional fibres orientated from approximately 30.degree. to approximately 70.degree. with respect to each other and substantially symmetrically with respect to the longitudinal axis of the vane along its span, and the intermediate layer comprises a set of essentially unidirectional fibres orientated substantially along the said longitudinal axis of the vane, at least one from among the vane root and vane tip exhibiting at least one laminated fastening tab comprising a pile of extensions of the layers of reinforcing fibres of the pressure face part and/or suction face part of the main vane section with at least one complementary pile of a central layer of essentially unidirectional reinforcing fibres orientated substantially parallel to those of the said intermediate layer in the corresponding vane root or vane tip, and between two plies of balanced fabric of reinforcing fibres, the warp of which is orientated substantially parallel to the unidirectional fibres of the said central layer. PA1 preparing, for example by cutting-out, the set of plies of fabric and/or webs and/or braids of reinforcing fibres, essentially dry, with the dimensions required to form the vane, PA1 laying-up the prepared elements with a defined laying-up method in order to fort the vane, around a core of synthetic lightweight material formed beforehand, so as to produce a vane preform having a core surrounded by a sheath of reinforcing fibres, PA1 arranging the preform in the injection mould, of the type having at least two complementary parts with complementary internal cavities corresponding to the shape of the vane, PA1 closing the mould in a sealed manner and creating a vacuum therein, PA1 injecting under pressure into the mould a thermosetting resin at an injection temperature for which the resin is substantially liquid and of low viscosity, preferably not greater than 100 mPa.s, and ensuring that all the layers of reinforcing fibres are impregnated, PA1 carrying out a cycle of polymerizing the resin and then, after cooling the mould and its contents, PA1 opening the mould and releasing the vane. PA1 compacting a core of lightweight cellular or foamed synthetic substance for each of the vanes of the flow-straightener, PA1 making a preform for each vane by laying-up layers of reinforcing fibres, previously prepared to the necessary dimensions, on the corresponding core, PA1 making a preform of the flow-straightener central body by laying-up and piling up the various layers of reinforcing fibres, previously prepared, which it includes, PA1 placing the preforms of the vanes and the preform of the flow-straightener body in an injection mould, PA1 laying-up, in the injection mould, layers of linking reinforcing fibres between the preforms of the vanes and of the flow-straightener body, PA1 closing the mould in a sealed fashion, creating a vacuum therein, preferably via the vane tips, and injecting a thermosetting resin at an injection temperature such that it has a low viscosity and is substantially liquid, then PA1 carrying out a polymerization cycle and finally releasing the flow-straightener from the mould.